This invention relates to a process for making a smooth, abrasion-resistant, nonstick, topographical support surface for a fabric and film forming device.
Nonwoven fabrics have been known for many years. In one process for producing nonwoven fabrics, a fiber batt or web is treated with streams or water, air, or other fluid to cause the fibers to entangle with each other and provide some strength in the batt. Many methods have been developed for treating fiber batts in this manner in an attempt to duplicate the physical properties and appearance of woven fabrics. Similarly, solid polymeric films may be treated by streams of water, air, or other fluid to create apertures in the film to allow for the passage of air or liquids through the film and to allow it to be used in a fashion similar to that of a nonwoven. Common uses for such apertured polymeric films include body-facing cover sheets for disposable absorbent articles, such as diapers, sanitary napkins, tampons, incontinence articles, and other absorbent articles.
U.S. Pat. Nos. 5,098,764 and 5,244,711 disclose backing members for supporting a fibrous web during the manufacture of nonwoven fabrics. The support members disclosed in U.S. Pat. No. 5,098,764 have a predetermined topography as well as a predetermined pattern of openings within that topography. In one specific embodiment, the backing member is three-dimensional and includes a plurality of pyramids disposed in a pattern over one surface of the backing member. This specific backing member further includes a plurality of openings which are disposed in the spaces, referred to as xe2x80x9cvalleysxe2x80x9d, between the aforementioned pyramids. In this process, a starting web of fiber is positioned on the topographical support member. The support member with the fibrous web thereon is passed under jets of high pressure fluid, typically water. The jets of water cause the fiber to intertwine and interentangle with each other in a particular pattern, based on the topographical configuration of the support member.
The pattern of topographical features and apertures in the support member is critical to the structure of the resulting nonwoven fabric. In addition, the support member must have sufficient structural integrity and strength to support a fibrous web while fluid jets rearrange the fibers and entangle them in their new arrangement to provide a stable fabric. The support member must not undergo any substantial distortion under the force of the fluid jets. Also, the support member must have means for removing the relatively large volumes of entangling fluid so as to prevent xe2x80x9cfloodingxe2x80x9d of the fibrous web, which would interfere with effective entangling. Typically, the support member includes drainage apertures which must be of a sufficiently small size to maintain the integrity of the fibrous web and prevent the loss of fiber through the forming surface. When the entangling fluid is air, and specifically, heated air, the forming surface must be resistant to the effects of the heated air; i.e., the forming surface must not melt or otherwise change form when subjected to the heated air. The forming surface should also be resistant to sticking of the fibrous web when heated air is used. In addition, the support member should be substantially free of burrs, hooks or the like irregularities that could interfere with the removal therefrom of the entangled fabric. At the same time, the support member must be such that fibers of the fibrous web being processed thereon are not washed away under the influence of the fluid jets.
Similarly, when the substrate to be treated by the streams of fluid or air is a polymeric film, the film may tend to stick to the forming surface, especially if the treating fluid is hot air or if the forming surface has any burrs, hooks, or other irregularities on its surface. The forming surface must thus be made with a very smooth surface to allow the apertured film to be drawn off easily and quickly during the forming process. Even when the apertured film does not stick to the forming surface, the process of heating the film may cause tiny amounts of polymer to be released from the film and stick to the forming surface. The tiny amounts of polymer may, over time, build up to create deposits of polymer on the forming surface. These deposits may alter the forming surface such that it is no longer usable. The forming surface should be easily cleanable so that the deposits can be easily and economically removed so that the forming surface may simply be cleaned and need not be replaced.
While machining may be used to fabricate such topographical support members, such a method of manufacture is extremely expensive and often results in aforementioned burrs, hooks and irregularities. Thus, there is a need for a method for making topographical support members which method is less expensive, reduces the numbers of burrs, hooks and irregularities therein, and produces a forming member with a surface which resists the formation of polymer deposits from the forming process, and which may be easily cleaned of such deposits.
This invention is directed to a method of forming an improved surface on a topographical support member for producing nonwoven fabrics and apertured films. More particularly, this invention provides an ion beam deposited coating to the surface of a topographical support member such that the coating is highly adherent and exhibits greatly improved wear resistance and environmental durability over a similar topographical support member without the coating.
Topographical support members may be fashioned with a very simple or a very intricate topographical pattern. Highly complex topographical surface patterns may be produced on the support member by engraving the-surface with a laser beam. When these support members with complex patterns are used to form apertured films or fabrics, the repetition of the aperturing process often causes a build-up of polymer from the film or fabric as it is being apertured on the surface of the support member as a by-product of the process. It has been found that even small amounts of polymer build-up interferes with the aperturing process and disrupts the desired pattern of the surface resulting in an inferior or unacceptable film or fabric product. Therefore, it was thought that any attempt to coat the topographical patterned surface would likewise distort or interrupt the pattern, making the topographical support member unsuitable for use.
Surprisingly, it has been found that the coatings made by the process of this invention do not distort the pattern of the support member surface, and that, in fact, the support member surface is actually enhanced by the coating. The coated surfaces of the invention not only resist the abrasive forces of normal wear, they resist polymer build-up which normally results from the aperturing process and are more easily cleaned when minor polymer build-up is experienced.
In accordance with the method of the present invention, a laser beam is directed onto a workpiece to be engraved with a topographical pattern. The laser beam is focused such that the focal point of the beam is below the top surface of the workpiece. The focusing of the laser beam at a point other than the top surface of the workpiece, e.g. at a point below the top surface, instead of on the surface is termed xe2x80x9cdefocusing.xe2x80x9d Thereafter, the defocused laser beam is used to drill a predetermined pattern of apertures in the workpiece. The defocused laser beam may also be used to form a topographical array of peaks and valleys surrounding at least some and preferably surrounding each aperture of the workpiece. The apertures may have substantially straight, parallel side walls or alternatively may have a tapered or conical-like top portion angled such that the major diameter of the aperture resides on the top surface of the resulting support member. The topographical array of peaks and valleys is formed by the center line to center line spacing of adjacent apertures being less than the major diameter of the top portion of the apertures. Such a spacing results in the taper of adjacent apertures intersecting within the starting thickness of the workpiece. The workpiece is then chemically cleaned to remove unwanted materials and other contaminants. Next, the workpiece is inserted into a vacuum chamber, the air in said chamber is evacuated and the workpiece surface is sputter-etched by a beam of energetic ions to assist in the removal of residual contaminants such as residual hydrocarbons and surface oxides, and to activate the surface. After the workpiece surface has been sputter-etched, a protective, abrasion-resistant coating is deposited using selected precursor gases by ion beam deposition. The ion beam-deposited coating may contain one or more layers. Once the chosen thickness of the coating has been achieved, the deposition process on the workpiece is terminated, the vacuum chamber pressure is increased to atmospheric pressure, and the coated workpieces having improved abrasion-resistance are removed from the vacuum chamber.
The present invention provides amorphous, conformal, protective, abrasion-resistant coats containing a combination of the elements selected from the group consisting of C, Si, H, O and N. More particularly, the coatings of the present invention are selected from at least one of the following combinations of elements: Si and C; Si, C and H; Si and N; Si, N and H; Si and O; Si, O and H; Si, O and N; Si, O, N and H; Si, C and N; Si, C, H and N; Si, C and O; Si, C, H and O; Si, C, O and N; and Si, C, H, O and N.
The process for deposition of these coatings uses an ion beam source which operates with-precursor gases comprising at least one of the following combinations of elements selected from the group consisting of Si and C; Si, C and H; Si and N; Si, N and H; Si and O; Si, O and H; Si, O and N; Si, O, N and H; Si, C and N; Si, C, H and N; Si, C and O; Si, C, H and O; Si, C, O and N; and Si, C, H, O and N. The process of the present invention is particularly well-suited to the manufacture of optically transparent coatings with tailored hardness, stress, and chemistry. These properties make the coatings of the present invention ideally suited to plastic substrates or workpieces, such as topographical forming surfaces for apertured films or nonwoven fabrics. Coatings which exhibit glass-like or quartz-like properties can be made by the present process. Coatings which have properties resembling silicon carbide, silicon nitride, and hydrogenated and oxygenated forms of these materials can also be made by this process.
Additionally, diamond-like carbon coatings can be made by the process of the present invention. The term xe2x80x9cdiamond-like carbonxe2x80x9d is meant to include amorphous materials composed of carbon and hydrogen, whose properties resemble, but do not duplicate, those of diamond. Some of these properties are high hardness (HV=about 1,000 to about 5,000 kg/mm2), low friction coefficient (approximately 0.1), transparency across the majority of the electromagnetic spectrum, and chemical inertness. At least some of the carbon atoms in DLC are bonded in chemical structures similar to that of diamond, but without long range crystal order. These DLC materials can contain to 50 atomic percent of hydrogen. The DLC coatings made by the present invention are hard, inert and slippery, and are ideal for use in many applications.
The coatings of the invention may range from about 50 xc3x85 to about 100 microns thick, depending upon the degree of abrasion resistance desired and upon the complexity and size of the forming member surface pattern. In general, the more complex the pattern, and the smaller the peaks and valleys of the forming member surface topography, the thinner the coating will need to be to avoid distortion of the surface pattern. Additionally, multiple layers of coatings may be provided, with each coating varying in thickness. For cases where a diamond-like carbon coating is required, it is preferred to deposit an interlayer material, or adhesion-promoting layer containing silicon atoms onto the substrate before deposition of the diamond-like carbon coating layer to ensure good adherence of the coating. Typically, the interlayer thickness is on the order of from 10 xc3x85 to 1 micron.